U.S. patent number 11,035,925 [Application Number 16/058,758] was granted by the patent office on 2021-06-15 for device, system, and method for controlling the focus of a laser to induce plasmas that emit signals with high directivity.
This patent grant is currently assigned to United States of America as represented by the Secretary of the Navy. The grantee listed for this patent is United States Government as represented by the Secretary of the Navy, United States Government as represented by the Secretary of the Navy. Invention is credited to Ryan P. Lu, Bienvenido Melvin L. Pascoguin, Ayax D. Ramirez.
United States Patent |
11,035,925 |
Pascoguin , et al. |
June 15, 2021 |
Device, system, and method for controlling the focus of a laser to
induce plasmas that emit signals with high directivity
Abstract
A focus controlling component is configured to control a focus
of a laser beam that passes through water and induces plasmas that
emit signals. The focus of the laser beam is controlled such that
the signals emitted by the induced plasmas interfere to form a
combined signal that propagates in a desired direction.
Inventors: |
Pascoguin; Bienvenido Melvin L.
(La Mesa, CA), Lu; Ryan P. (San Diego, CA), Ramirez; Ayax
D. (Chula Vista, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
United States Government as represented by the Secretary of the
Navy |
San Diego |
CA |
US |
|
|
Assignee: |
United States of America as
represented by the Secretary of the Navy (Washington,
DC)
|
Family
ID: |
1000005617981 |
Appl.
No.: |
16/058,758 |
Filed: |
August 8, 2018 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20200049788 A1 |
Feb 13, 2020 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S
15/88 (20130101); G01S 1/76 (20130101); H01J
37/32412 (20130101) |
Current International
Class: |
G01S
1/76 (20060101); G01S 15/88 (20060101); H01J
37/32 (20060101) |
Field of
Search: |
;367/131 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Moreno et al., "Encoding generalized phase functions on Dammann
gratings," Opt. Lett. 35, 1536-1538 (2010). cited by applicant
.
Davis et al., "Fourier transform pupil functions for modifying the
depth of focus of optical imaging systems," Appl. Opt. 48,
4893-4898 (2009). cited by applicant .
Brelet et al., "Underwater acoustic signals induced by intense
ultrashort laser pulse," The Journal of the Acoustical Society of
America 137, EL288 (2015). cited by applicant .
Wang et al., "Creation of identical multiple focal spots with
three-dimensional arbitrary shifting," Optics Express, vol. 25, No.
15 (2017). cited by applicant.
|
Primary Examiner: Murphy; Daniel L
Attorney, Agent or Firm: Naval Information Warfare Center,
Pacific Eppele; Kyle Pangallo; Matthew D.
Government Interests
FEDERALLY-SPONSORED RESEARCH AND DEVELOPMENT
The United States Government has ownership rights in this
invention. Licensing inquiries may be directed to Office of
Research and Technical Applications, Space and Naval Warfare
Systems Center, Pacific, Code 72120, San Diego, Calif., 92152;
telephone (619) 553-5118; email: ssc pac t2@t2@navy.mil,
referencing NC 103667.
Claims
What is claimed is:
1. A device, comprising: a focus controlling component configured
to control a focus of a laser beam that passes through water and
induces plasmas that emit signals, wherein the focus of the laser
beam is controlled such that the signals emitted by the induced
plasmas interfere to form a combined signal that propagates in a
desired direction.
2. The device of claim 1, wherein the focus controlling component
causes the focus of the laser beam to have a focal pattern that is
three dimensional with multiple foci.
3. The device of claim 2, wherein the focus controlling component
is configured to adjust the focal pattern of the laser beam to
adjust the desired direction of propagation of the combined
signal.
4. The device of claim 1, wherein the focus controlling component
controls the focus of the laser beam such that the induced plasmas
are shaped such that the emitted signals interfere to form the
combined signal that propagates in the desired direction.
5. The device of claim 1, wherein the focus controlling component
is a phase mask.
6. The device of claim 5, wherein the phase mask includes a
computer controlled spatial light modulator.
7. The device of claim 5, wherein the phase mask includes multiple
diffraction gratings.
8. The device of claim 7, wherein the multiple diffraction gratings
control the focus of the laser beam such that the focal pattern has
a fractal shape.
9. The device of claim 5, wherein the phase mask includes multiple
liquid crystal spatial light modulators.
10. The device of claim 1, wherein the focus controlling component
includes a computer-controlled beam rasterizer.
11. A system, comprising: a laser source configured to generate and
output a laser beam; and a focus controlling component configured
to control a focus of the laser beam to have a three dimensional
focal pattern with multiple foci, such that as the laser beams
passes through water, plasmas are induced that emit signals that
interfere to form a combined signal that propagates in a desired
direction.
12. The system of claim 11, wherein the plasmas emit sonar
signals.
13. The system of claim 11, wherein the plasmas emit
electromagnetic signals.
14. The system of claim 11, wherein the focus controlling component
is a phase mask.
15. The system of claim 14, wherein the phase mask causes the
multiple foci to be produced simultaneously.
16. The system of claim 15, wherein the phase mask includes at
least one of a liquid crystal spatial light modulator, a deformable
mirror, a hologram grating, and an etch crystal grating.
17. The system of claim 11, wherein the focus controlling component
includes a computer-controlled beam rasterizer.
18. A method, comprising: generating a laser beam; controlling a
focus of the laser beam to have a three dimensional focal pattern
with multiple foci; and passing the laser beam through water to
induce plasmas that emit sonar signals, wherein the sonar signals
interfere to form a combined sonar signal that propagates in a
desired direction.
19. The method of claim 18, wherein the focus of the laser beam is
controlled so that the induced plasmas are shaped to emit the sonar
signals that interfere to form the combined sonar signal that
propagates in the desired direction.
20. The method of claim 19, further comprising adjusting the
direction of propagation of the combined sonar signal by adjusting
the focal pattern.
Description
FIELD OF THE INVENTION
The present invention pertains generally to laser induced signal
emitting plasmas. More particularly, the present invention pertains
to controlling a focus of a laser to induce plasmas under water
that emit signals with high directivity.
BACKGROUND
Research has shown that underwater sonar sources may be generated
by pulsing laser beams into water. With a laser-based approach,
lasers may be directed toward the water remotely, and no hardware
needs to touch the water. This provides for a stealthy and durable
way for aircraft to communicate with submarines.
When a laser beam penetrates the surface of the water, it causes
the molecules around it to turn into superhot plasma. This forces
some of the electrons in the molecules to break free, ionizing the
water and causing it to expand in a shock wave. These waves can
then be detected by acoustic sensors in the water. In this manner,
lasers have been shown to produce underwater sonar sources.
Generation of a sonar source by a laser may be understood with
reference to FIG. 1. As shown in FIG. 1, a high energy laser beam
120 that is on the order of approximately 10-100 joules is
generated by a laser source 110. The laser beam is focused towards
water. Due to the Kerr effect, the high energetic laser beam 120
induces a series of plasmas 130 as it passes through the water. The
plasmas 130 emit signals 140 including sonar signals and
electromagnetic signals.
In the system shown in FIG. 1, the laser beam 120 is directed
towards a single point in the water. This, in turn induces plasmas
130 having a circular shape. As can be seen from FIG. 1, as a
result, the signals 140 emitted by the plasmas 130 are isotropic.
That is, the signals 140 radiate from the plasmas 130 with equal
strength in all directions. Accordingly, the laser generated
underwater sonar signals have a low directivity. As a result, the
sonar signals are sent to too many locations, and the probability
of interception of the sonar signals by unintended recipients is
high.
In view of the above, it would be desirable to ensure that a laser
generated signal under water only arrives at the intended
target.
SUMMARY
According to an illustrative embodiment, a focus controlling
component is configured to control a focus of a laser beam that
passes through water and induces plasmas that emit signals. The
focus of the laser beam is controlled such that the signals emitted
by the induced plasmas interfere to form a combined signal that
propagates in a desired direction.
These, as well as other objects, features and benefits will now
become clear from a review of the following detailed description,
the illustrative embodiments, and the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The novel features of the present invention will be best understood
from the accompanying drawings, taken in conjunction with the
accompanying description, in which similarly-referenced characters
refer to similarly-referenced parts, and in which:
FIG. 1 illustrates a conventional system for generating a sonar
source under water using a laser.
FIG. 2 illustrates a system for generating a sonar source under
water using a laser with a controlled focus according to an
illustrative embodiment.
FIGS. 3A and 3C illustrate diffraction gratings for controlling a
focus of a laser beam.
FIGS. 3B and 3D illustrate one-dimensional and two-dimensional
focal patterns produced using the diffraction gratings shown in
FIGS. 3A and 3C, respectively.
FIG. 4 illustrates a laser beam having multiple foci in an axial z
direction.
FIG. 5 is a flow chart depicting a process for generating a sonar
source with high directivity according to an illustrative
embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
According to an illustrative embodiment, plasmas are induced by a
laser in water in a manner such that signals emitted by the plasmas
form a combined signal having a desired propagation direction. This
is achieved by using a focus controlling component to control the
focus of the laser beam to have a three dimensional focal pattern
with multiple foci. By selecting and adjusting the focal pattern,
the shape of the induced plasma can be controlled to cause the
plasma to emit signals with high directivity. These emitted signals
interfere to form the combined signal that propagates in a desired
direction. In this manner, the combined signal formed from the
signals emitted by the plasmas can be steered and refined as
desired. This ensures that the combined signal only arrives at the
intended target.
FIG. 2 illustrates a system for generating a sonar source under
water using a laser with a controlled focus according to an
illustrative embodiment. The system includes a high power laser
source 210 configured to generate and output a laser beam 220. The
laser source 210 may be any commercial laser source that emits
lasers having a power of 10-100 joules.
The system also includes a focus controlling component 225
configured to control the focus of the laser beam 220. The laser
source 210 and/or the focus controlling component 225 may be
located in air or another gaseous medium, with the laser beam 220
directed toward a water surface. Alternatively, the laser source
210 may be located in water along with the focus controlling
component 225, and the laser beam 220 may propagate through water
from the laser source 210 after passing through the focus
controlling component 225.
As the laser beam 220 passes through the water, it induces plasmas
230. As explained in further detail below, the plasmas 230 emit
signals 240 including sonar and electromagnetic signals that have a
high directivity.
In the embodiment shown in FIG. 2, the focus controlling component
225 is a high energy phase mask that controls the focus of the
laser beam 220 to have a three dimensional focal pattern with
multiple foci at different locations. The multiple foci may have
different intensities. The phase mask may include phase inducing
components such as liquid crystals, deformable mirrors, holograms,
etch crystals, etc.
To aid in understanding of how phase inducing components may be
used to control the focus of a laser beam, examples of liquid
crystal Daman diffraction gratings are shown in FIGS. 3A and 3C.
The diffraction grating 310 shown in FIG. 3A has a one-dimensional
diffraction pattern, while the diffraction grating 320 shown in
FIG. 3C has a two-dimensional diffraction pattern. The diffraction
gratings cause the laser to focus at multiple points in a two
dimensional plane. Passing a laser beam through the diffraction
grating 310 shown in FIG. 3A causes the laser to have a focal
pattern 330 having the foci along a single axis, e.g., an x axis,
as shown in FIG. 3B. Passing a laser beam through the diffraction
grating 320 shown in FIG. 3C causes the laser to have a focal
pattern 340 having foci distributed in a two-dimensional array,
e.g., foci distributed in the x-y plane as shown in FIG. 3D.
According to an illustrative embodiment, diffraction gratings such
as those shown in FIGS. 3A and 3C may be combined to form a phase
mask that allows the optical depth of the laser beam's focus to be
extended. A phase mask allows the focal pattern of a laser to be
controlled such that foci may be distributed not just in two
dimensions but also in a third dimension, e.g., along the z
axis.
This may be understood with reference to FIG. 4 which illustrates a
laser beam having a focal pattern 400 with multiple foci in an
axial z direction. For example, the "bright" spot 410 shown in FIG.
4 represents one focal point along the z axis, while the "dimmer"
spots 420 represent another focal point along the z axis.
According to illustrative embodiments, controlling the focus of the
laser beam to have a three dimensional focal pattern with multiple
foci allows for control of the shape of the plasmas 230 induced by
the laser as it passes through water. That is, as shown in FIG. 2,
the plasmas 230 need not be circular like the plasmas 130 shown in
FIG. 1. For example, as shown in FIG. 2, the plasmas 230 may be
elliptical. It should be appreciated that the shape of the induced
plasmas may be controlled to be any desired shape by selecting an
appropriate focal pattern for the laser beam 220.
As the induced plasmas 230 are not circular, the
sonar/electromagnetic signals 240 emitted from the plasmas 230 will
not be isotropic (in the same direction) like the
sonar/electromagnetic signals 140 shown in FIG. 1. Rather, the
sonar/electromagnetic signals 240 emitted by the plasmas 230 will
have a high directivity, radiating in different directions. The
signals 240 will interfere with each other to produce a combined
sonar/electromagnetic signal 250 that propagates in at least one
certain desired direction, as indicated by the arrows on the
combined sonar/electromagnetic signal 250.
The focal pattern of the laser beam 220 determines the shape of the
plasmas 230, and the shape of the plasmas determine the directions
of the emitted signals 240 and the direction of propagation of the
combined signal 250 formed from the emitted signals. Thus, by
selecting and adjusting the focal pattern using the focus
controlling component 225, a user may select and adjust a direction
of propagation of the combined signal. Accordingly, the laser beam
may be used efficiently to control the direction of propagation of
the combined signal.
According to one embodiment, the focus controlling component 225 is
a phase mask that has a defined combination of gratings that cause
the laser beam to have a three dimensional focal pattern. Gratings
which individually would produce given focal patterns can be
stacked to produce a new three dimensional focal pattern.
Additional gratings can be added over and over to generate a
fractal effect, thus causing the laser beam to have a fractal focal
pattern.
Instead of or in addition to the gratings, the phase mask may
include one or more spatial light modulators that cause the laser
beam to have a focal pattern with multiple foci in the
z-direction.
The gratings or spatial light modulators may be replaced or
switched to alter the focal pattern of the laser beam and thus the
propagation direction of the combined signal formed by the signals
240 emitted by the plasmas 230.
According to another embodiment, a computer controlled phase mask,
such as a computer controlled spatial light modulator, can be
utilized to change the phase mask design in real time. This allows
the focal pattern of the laser beam to be altered in real time,
thus altering the direction of propagation of the combined signal
formed from the signals emitted by the plasmas 230.
An advantage of a phase mask is that the foci are generated
simultaneously. However, although not shown in FIG. 2, it should be
appreciated that a computer-controller rasterizer may be used
instead of the phase mask to control the focus of the laser beam
220. A computer-controlled rasterizer is more design friendly than
a phase mask as it does not require complex computations and
experiments that are needed to design a phase mask that results in
the desired three dimensional foci.
FIG. 5 is a flow chart showing steps of a process for generating a
sonar source with high directivity according to an illustrative
embodiment. It should be appreciated that the fewer, additional, or
alternative steps may also be involved in the process and/or some
steps may occur in a different order.
Referring to FIG. 5, the process 500 begins at step 510 at which a
laser beam is generated by any suitable high power laser source,
e.g., the laser source 210 shown in FIG. 2. At step 520, a focus of
the laser beam is controlled to have a three dimensional focal
pattern with multiple foci. This step may be performed by a focus
controlling component, such as the phase mask focus controlling
component 225 shown in FIG. 2. At step 530, the laser beam is
passed through water to induce plasmas that emit signals that form
a combined signal that propagates in a desired direction.
Although not shown, it should be appreciated that an additional
step may be included for adjusting the focal pattern of the laser
beam as desired so as to adjust the direction of propagation of the
combined signal.
It will be understood that many additional changes in the details,
materials, steps and arrangement of parts, which have been herein
described and illustrated to explain the nature of the invention,
may be made by those skilled in the art within the principle and
scope of the invention as expressed in the appended claims.
* * * * *